Safety combustion control system



Aug. 14, 1962 p, BREDESEN ETAL 3,049,169

- SAFETY COMBUSTION CONTROL SYSTEM 2 Sheets-Sheet 1 Filed June 9, 1958FIG. I

5|a. ADJUSTING mos UNIDIEECTIONAL. DRNE' INVENTORS. PHILIP N. BIZEOESENBY GEOQGE 6. OUTTEQSON ATTOENEYi 1962 P. N. BREDESEN ETAL 3,049,169

SAFETY COMBUSTION CONTROL SYSTEM Filed June 9, 1958 2 Sheets-Sheet 2 iFIG. 3 54 (T) T TE?) (I) T INVENTORS PHILIP N. BREDESEN BY GEORGE G.OUTTERSON 36 1 65, l a/12 f 4 38am ATTORNEYS United States PatentOflfice 3,649,159 Patented Aug. 14, 1962 3,049,16? SAFETY (IGMEUSTION(IQNTRGL SYSTER i Philip N. Bredesen, 4865 Cvster Road, Lorain, Ohio,and

George G. Gutterson, 3 .19% (Jar-Eton Drive, Bay Village, Ohio FiledJune 9, 1958, Ser. No. 740,887 (Ilaims. (Cl. 158-43) The presentinvention relates to control for a combustion system, for example of theoil or gas-fired type and in which various devices such as ignition andfuel supplying means are sequentially controlled. More particularly theinvention relates to control systems for producing a predetermined cyclefor setting into operation and controlling the operation of fuel supplyand safety control mechanisms, and pilots, blowers, alarms, and thelike, for assuring proper and safe operation.

Heretofore there has been a difiiculty in such equipment in that it haslacked versatility, not being capable, without great modification, ofmeeting varied job requirements.

It is an object of the present invention to provide simple andinexpensive means for overcoming the above mentioned difliculty.

The invention is defined in the appended claims when read in the lightof the following description of preferred embodiments, all of whichemploy separate circuits to energize a timer motor and an electricclutch to operate cam switches and provide advantages of greaterversatility as will hereafter become evident.

Other objects and advantages will become apparent and the invention willbe better understood from consideration of the following descriptiontaken in connection with the accompanying drawing, in which:

FIG. 1 is a schematic diagram of a typical control system for an oil orgas-fired furnace embodying the present invention; 1

FIG. 2 is a simplified diagram of a portion of the circut shown in FIG.1, and

FIGS. 3 through 8 illustrate modifications.

Referring first to FIG. 1, there is shown a preferred embodiment of theinvention adapted to operate furnace equipment when a source of controlpower is connected to lines 11 and 12 and other events occur asexplained below.

Connected across lines 11 and 12 is a step-down transformer primarywinding 16. The transformer secondary 17 provides low voltage for acircuit including the operating winding 18 of a safety switch 20 havinga normally closed contact 21 in the circuit of the transformer primary16 and a normally open contact 22 in the circuit of an alarm device 23connected in series with the contact 22 across the lines 1112. Switch 29may be a time delay relay, e.g., having a dashpot 24, and this has beenfound to provide improved performance over a bimetal thermostat switchoperated by a heater coil as disclosed and claimed in US. Patent2,673,603 issued March 30, 1954 to George G. Outterson. Switch winding18 may be hooked into a portion of a balance bridge involving a centertap 26 on the secondary 17 with the secondary winding portions A and Bthus formed connected back through other equipment somewhat as describedand claimed in said patent or as described hereinafter.

As shown in FIG. 1 of the present application, the transformer isprovided with a second secondary 27 connected to energize an amplifier28 for a flame detector 29. Flame detector 29 may take the form of athermocouple, or thermistor, or metal helix, or electric eye, and it andits amplifier may be conventional items. The output of the flamedetector amplifier 28 energizes coil 30 of a flame relay 31 havingnormally open contacts '32 and 33 and normally closed contacts 34 and35.

The far end of the A portion of secondary 17 is connected through aresistor impedance 36 and no. contact 32 to a point 37 to form the topleg of the bridge. The safety switch coil 18 is connected across points26 and 37 to form the middle portion of the bridge, while the far end ofthe secondary winding portion B is connected through a time delay device40 which, for simplicity, may be a thermistor, and this circuit (for thebottom leg of the bridge) is completed through a coil 42 of a masterrelay 43 and the heat demand responsive contact 44 of a thermostat 4Sand back through the flame relay n.c. contact 34 and then (when 30 isdeenergized) back to the balance bridge common junction 37.

The master relay 4% is provided with an no. contact 46 which shorts outthe flame relay contact 34, and the main relay is also provided with anno. contact 47 contacted in series with line 11 and serving to energizefinal equipment as hereafter explained. An additional contact 48 mayalso be included for possible use as later described for FIG. 8.

As suggested in US. Patent 2,655,207 issued October 13, 1953 upon anapplication filed by G. G. Outterson, the equipment is provided with atimer motor T and a timer cam 51 for actuating timer cam switches 52 and53. In accordance with the present invention the system differs in thatthere is also provided a limit switch 54 in the circuit of the motor tolimit travel of the driven cam without requiring the motor T to stall,and an electrically operated clutch C is energized by a circuitseparated from the circuit through the limit switch and thus to thetimer motor, and the connections to final equipment are different as maybe more apparent from consideration of FIG. 2 which is a simplifieddiagram of a portion of the circuit of FIG. 1. It will be understoodthat the motor T is preferably as light, inexpensive, and compact aspossible, with the windings of minimum resistance for a maximumelectrical efliciency so that it is in danger of overheating and burningout if allowed to stall.

Preferably reduction gearing RG is used and it may conveniently beinterposed between T and C to assure that the cam 51 will not drive backthrough the motor T whenever the clutch is engaged, but the motorde-energized.

With the embodiment shown in FIGS. 1 and 2, when the clutch is energizedthe cam 51 is driven by T unidirectionally in the direction indicated bythe small arrows, but as the clutch C is de-energized the cam is forcedto return to the starting (or t position as by the action of a smallspring 55 which may be attached either to the shaft driving the same(FIG. 1) or to the cam 51 itself (FIG. 2). In accordance with thepresent invention the cam is sometimes driven to limit at which time thelimit switch 54 is provided to de-energize the motor, which prevents itfrom overheating or burning out or overstressing the mechanicalconnections in the mechanism. Limit switch 54 may be a simple leafswitch attached to the shaft driving the cam 51 with an associaterelatively stationary cam 51a made adjustable so that post-purge timingi.e., time required after a normal cycle of attempted furnace firing andfor getting rid of raw gases or exhausted products of combustion beforestarting a new light-up and firing cycle in the event of flame failureduring the previous cycle, contact 31 remaining closed, can be varied byadjusting the position of such relatively stationary cam.

As described and illustrated in the above mentioned Patent 2,655,207,cam follower means may be provided to assure that the timer cam switches52 and 53 will be operated only during motor driven cam advance and willnot operate during cam return under the influence of the spring 55.

As described in the above mentioned Patent 2,655,207, and also in U.S.Patent 2,655,208, the control equipment may be used to operate a mainfuel valve V, a blower B, and a flame ignition device I as well as thetimer T and clutch C. With an arrangement as shown in FIGS. 1 and 2 ofthe present application, clutch C is energized across the same lines asthe ignition I, and interconnections are made from the main relaycontact 47 through the flame relay contacts 35 and 33 and through thecam contacts 52 and 53 and through the driven equipment in such mannerthat as heat demand causes the thermostat contact 44 to close, and asthis closes the master relay 43, a circuit may be traced through line11, master relay contact 47, and (if no fire) through flame relaycontact 31 to energize T, C and I. Regardless of position of the flamerelay, blower B is also energized and this will purge the system of anyexhausted gases in a normal starting sequence.

All of the above may be thought of as occurring at time t (equal to zeroseconds), and at a time t (which for FIGS. 1 and 2 might be assumed tobe five seconds later) cam switches 52 and 53 close. Cam switch 52'serves to hold the timer T, clutch C and ignition I regardless ofoperation of flame relay 31 and consequent opening of its normallyclosed contact 35. Cam switch 53 serves to energize valve V (unlessflame relay operation has already done so). Valve V is assumed to be asolenoid operated valve for the purpose of admitting main fuel to thefurnace and it will be seen from FIGS. 1 and 2 that cam switch 53 isshorted out by flame relay contact 3-3 whenever the flame relay coil 30is energized. At time 13 (which for FIGS. 1 and 2 might be assumed to be15 seconds later than time t cam switches 52 and 5-3 reopen leavingvalve V under control of the flame relay, and leaving T, C and Ide-energized unless the flame relay drops out to cause recycling. When Cis de-energized the cam returns under the influence of the springwithout disturbing the cam switches as already explained.

Any tripping of the safety switch 20' will de-energize the flamedetector amplifier 28 and all the low voltage circuits and provide analarm through device 23, but otherwise the equipment is powered in suchmanner that final equipment energization is dependent upon flamedetection but with all timing operations (except post purge) dependentupon clutch control of cam switches.

FIG. 2.Operatin: Failure to Ignite During startup the master relay 43powers the blower,

ignition, clutch and timer. From time t to a trial for ignition is made.Upon failing to ignite, the timer continues until stopped by the camlimit switch 54 at a full limit position where the cam will remainbecause held by the clutch and motor gearing until a time z when thesafety switch trips and opens the low voltage circuits. Until thishappens the blower B continues purging gases to leave the system in safecondition for making another trial when the safety switch is reset bythe button 57, as hereinafter explained.

Thermistor 40 is in the circuit to give a short delay each time relay 43is operated (in order to allow a safety check on the flame relay, forexample if a power failure has occurred) but this feature could beomitted. Basically the low voltage circuit is a bridge with the coil 18of the safety switch 20 in the center. If the thermostat 45 is closedand the master relay 43 has operated and the flame relay has pulled in,the bridge will be balanced and no current will flow through 18. But ifthe flame relay does not close, current will continue in coil 18 untilthe time (fixed by the selection of components of the bridge circuit)when tripping occurs. Furthermore, any fault in the circuit which causesbridge unbalance will ultimately trip safety switch 20. Thisde-energizes all of the equipment except the alarm which is thenenergized. A button 57 may be provided so that the safety switch can bemanually reset in order to make a new try.

FIG. 2.Operati0n: Flame FailureAfter Igniting It will be observed thatwith the arrangement described, if there is any flame failure duringfiring the flame relay 31 will drop out, recycling the system in normalmanner. Whenever flame is established, firing will continue normally,but if a flame is not established a lock-out oc curs. During normaloperation furnace firing continues with heat demand, and at the end ofheat demand thermostat 44 opens to de-energize master relay 43 and thisin turn de-energizes fuel valve V and blower B.

FIG. 3

A modification is shown in FIG. 3 where the arrangement is the same asin FIG. 2 except that the clutch C is powered directly from the M.R.contact 47. This means that whenever the master relay is pulled in theclutch is energized and thus the timer cam is held at the position allduring firing. This prevents recycling in the event of flame failure.

FIG. 4

Another modification is shown in FIG. 4 where the blower is againconnected across the line from the master relay contact 47, but where apilot fuel valve solenoid P is connected in parallel with the ignition Ito be en ergized only by the cam switch 5-2 (from time i to t and notindependently by the flame relay. The main valve V is controlled by theflame relay contact 33 alone while the timer motor and clutch are underthe influence of both the normally closed RR. contact 35 and one of thecam switches (in this case 53). Thus the master relay contact 47 firstpowers the blower, timer and clutch. At time t cam switch 52 powers thepilot solenoid and ignition while cam switch 53 maintains the timer andclutch when the flame relay pulls in. Operation of the flame relay willalso energize V to open the main fuel supply. At time i the ignition isout OE (and the pilot solenoid de-energized) and the timer and clutchare deenergized. The cam then returns to zero and remains there duringfiring.

FIG. 4.-Failure to Ignite If there is a failure to ignite during startupwith the arrangement of FIG. 4, the cam is driven to the limit andlock-out occurs when the safety switch trips. Such failure of pilot toignite also prevents trial for main flame inasmuch as the contact 33never closes. Although the flame detector may normally see both pilotand main flame, so that if thepilot lights the flame relay will pull in,the pilot is eventually turned ofi as the cam contact 52 opens and if atthat time the main flame is not yet established the flame relay willdrop out, the main fuel valve will be turned off, the cam drives tolimithndlockout occurs.

FIG. 4.Flame Failure After Igniting If there is a flame failure duringfiring the flame relay drops out and re-initiates a normal startingcycle. If ignition does not take place during the first recycle, lockoutoccurs as described above under the heading FIG. 4Failure to Ignite.

FIG. 5

. Another modification is shown in FIG. 5 where M.R. 47 again powers theblower and through a single cam operated contact 52 powers the pilotsolenoid (P) and ignition (I). The flame relay contact 33 controls themain valve (V) while the clutch (C), and timer (T) in series with limitswitch 54, are connected across the line formed by the contact 47. Attime t the pilot solenoid and the ignition are powered and when flame.is established, FR 33 closes turning on the main fuel. At time a, thepilot and ignition are turned off, the cam drives to limit and is heldthereby the clutch during the remainder of the heating cycle (that isuntil a time t when the thermostat 45 opens to de-energize the masterrelay).

If there is a failure to ignite during startup, the result is the sameas for the embodiment of FIG. 4.

If there is a flame failure during firing with the arrangement of FIG. 5the flame relay drops out and lockout occurs as the safety switch trips.There is no recycling.

FIG. 6

Another modification is illustrated in FIG. 6 where the arrangement isassumed the same as in FIG. 5 except the second cam switch 53 isconnected in series with flame relay contact 33 in the line of the valveV. With such an arrangement the master relay powers the blower, thetimer, and the clutch and at time t the pilot and the ignition areenergized through the cam contact 52. If a fuel valve delay is desired,contact 53 may be displaced a required number of degrees around the camfrom the contact 52. This establishes what might be thought of as a newtime t when contact 53 closes and the main fuel flows if the pilot hasbeen proved. At a time cam contact 52 opens and the ignition is turnedofl. The cam drives to limit and the clutch holds throughout the firingcycle although the timer motor is de-energized by limit switch 54 whenthis limit is reached. With the arrangement of FIG. 6 if there is afailure to ignite during startup the result is the same as for FIG. 4except that the trial for main flame occurs from time 1 to t If there isa flame failure during firing, the result with the arrangement of FIG. 6is the same as that of the arrangement of FIG. 5.

FIG. 7

In the modification of FIG. 7 the arrangement is the same as in FIG. 5except that an extra contact 48 on ta Without the clutch energized. Thuscam 70 maintains the blower until the timing cycle is complete, allowingpurging of gases.

FIG. 7.-Failure t0 Ignite If the pilot fails to ignite, the cam drivesto limit and the master relay drops out when safety lock-out occurs. Butthe usual post purge cycle carries through. If the main flame fails toestablish, the ignition is turned off, the flame relay is de-energized,contact 33 opens, and the cycle described immediately above occurs.Trial for main flame occurs from time t to 2 FIG. 7.Flame Failure AfterIgnition If there is a flame failure during firing, the flame relaydrops out. This turns ofl the main fuel and deenergizes the master relaybut the post purge cycle follows. There is no recycling.

FIG. 8

Summary of Operation A summary of typical operation and advantages forthe various embodiments is illustrated in the following table.

TABULAR SUMINIARY OF TYPICAL OPERATION Direct Ignition Fuel Valve DelayPre Ignition Recycling Non Recycling. Pre Purge Pilot Proving Post PurgeNotes:

(*)If pilot is proved.

tx-Emergency shut-off when safety switch trips. tnN0rmal shutdown whenthermostat opens.

M.R. 43- (see FIG. 1) is connected to separately energize circuits to C,and through 33 to V, and through 52 to P and I, and an additional camswitch 70 is connected in parallel across master relay contact 47 tooperate as a post purge contact. This cam switch 73 is arranged to beoperated by a cam directly on the motor or gear shaft (rather thanthrough the clutch) and, unlike the limit switch 54 which is arranged toopen at the limit of cam travel the cam switch 70 is assumed set toclose at a time ti (shortly after initiation of the cam control timingcycle) and to stay closed throughout the timing cycle. At time t contact52 closes to energize the pilot solenoid and the ignition and then, asthe flame relay pulls-in, valve V is energized to turn on the main fuelif the pilot is proved. The cam then drives to limit which is set tosatisfy the post purge timing requirement. After the heat demand ends,the master relay drops out, the cam 51 (FIG. 1) returns to zero, and thetimer starts up again There is thus provided arrangements of the classdescribed capable of meeting objects as above set forth, andadvantageous from many standpoints and particularly in permitting amanufacturer to produce one basic control which, with only very slightmodifications readily made in the field, can be used to operate diverseinstallations varying from simple space heating units to furnaces 7means across which an AC. potential may be impressed, a first switch, atransformer having a primary Winding connected through said first switchacross said terminal means and having a low voltage secondary winding, athermostat switch, a master relay having a coil connected in series withsaid thermostat switch and at least a portion of said secondary windingand having at least one normally open contact, a flame relay having acoil arranged to be energized responsive to flame detection and havingat least one normally open contact and at least one normally closedcontact, means including connections for energizing the air supply meansthrough the normally open contact of said master relay, means includingconnections for energizing the fuel supply means through the normallyopen contact of said master relay and electrically coupled in seriescircuit through the normally open contact of said flame relay, and meansincluding connections for energizing the ignition means and including atleast the normally open contact of said master relay, the combination ofa timer motor Which overheats if stalled, means including reductiongearing driven by the timer motor and through which the motor cannot bedriven, means including an electric clutch driven by the gearing whenthe motor is energized, a cam shaft and a cam carried thereby, meansoperably coupling the cam shaft to be driven by the clutch from aninitial position when the motor and clutch are energized, spring meansfor returning the cam to the initial position when the clutch isde-energized, normally open cam-operated switch means arranged to beclosed and to be opened by the cam when it is driven unidirectionally bythe motor, a limit switch on the cam shaft and electrically connected inseries with the timer motor to prevent cam overtravel, means includingconnections and at least the normally open contact of said master relayfor energizing the series circuit of the motor and the limit switch,means including connections and at least the normally open contact ofthe master relay for energizing the clutch, and means includingconnections through said cam operated switch means for energizing theignition means independent of the flame relay and in timed sequence withrespect to the energization of the air supply means.

2. In a combustion control system of the type having a master relay andhaving fuel supply, air supply and ignition electrically operated underthe control of a normally open contact of the master relay, and having aflame relay with normally open and normally closed contacts, and havinga unidirectional operative timer motor which overheats if stalled, thecombination of means including a reducing gear driven by the motor, acam shaft and cam and associated cam-operated switch means, a springbiasing the cam to an initial position, an electrically operated clutchoperably interposed between the reducing gear and the cam shaft foralternatively holding the cam through the gears or allowing the cam toreturn under the influence of the spring, a hrnit switch arranged to beoperated by the cam shaft and electrically connected in series with thetimer motor for preventing lovertravel of the cam, means includingconnections through the normally open contacts of said master relay tooperate the air supply, means including connections through the normallyopen contact of said master relay in series with the normally closedcontact of said flame relay with a branch circuit fiom the normally opencontact of said master relay through at least a portion of the camoperated switch means for energizing the ignition and for energizing theseries circuit of the limit switch and the timer motor, and meansincluding connections through the normally open contact of said masterrelay in series with the normally open contact of said flame relay with-a branch circuit from the normally open contact means of said masterrelay through at least a portion of the cam operated switch means toenergize the fuel supply, and means including connections for energizingthe clutch at least responsive to master relay energization.

3. In a combustion system of the type having a master relay with anormally open contact and having fuel sup ply control, air supplycontrol, and ignition control all electrically operated under thecontrol of the normally open contact of the master relay, and having aflame relay including a normally open contact and a normally closedcontact, and having a unidirectionally operative timer motor whichoverheats if stalled, the combination of means including reducing gearsdriven by the motor, means including a cam shaft driven by the gears,plural cam=operated switches normally open and arranged to betemporarily closed by the cam, a spring for returning the cam shaft toan initial position, an electrically oper ated clutch interposed betweenthe gearing and the cam shaft and operative to alternatively hold thecam shaft through the gears or to allow it to return under the influenceof the spring, a cam-shaft operated limit switch electrically connectedin series with the timer motor for preventing overtravel of the cam,means including connections through the air supply, means includingconnections through the normally open contact of the master relay and inseries connection through one of the cam operated switches forenergizing the ignition, means including connections through thenormally open contact of the master relay in series connection with thenormally open contact of the flame relay to operate the fuel' supply,and means including connections for energizing the clutch responsive tomaster relay energization.

4. The combination as in claim 3 further characterized a and timer motorthrough the normally closed flame relay contact independently .ofoperation of the cam switches, thereby to provide direct ignition, fuelvalve delay, preignition and recycling.

5. The combination as in claim 3 further characterized by the clutchbeing connected to be energized directly by the normally open contact ofthe master relay, the series circuit of timer motor and limit switchbeing connected in parallel with the ignition and thereby energized fromone of the cam operated switches but with the ignition and seriescircuit of limit switch and timer motor also arranged for energizationthrough a branch circuit including the normally closed flame relaycontact to energize the same independently of operation of the camswitches, and there being means including a branch circuit to operatethe fuel supply through one of the cam operated switches independentlyof energization of the flame relay, thereby to provide direct ignition,fuel valve delay, pre-ignition, nonrecycling and prepurge.

6. The combination as in claim 3 further characterized by there beingconnections to operate the air supply directly through the normally opencontact of the master relay, a pilot fuel supply control means, thepilot fuel supply control means being connected in parallel with theignition, the series circuit of the limit switch and timer motor beingplaced in parallel with the clutch and these circuits together beingarranged for alternative energization through the normally open camcontacts, thereby to provide pre-ignition, recychng, prepurge and pilotproving.

7. The combination as in claim 3 further characterized by there beingconnections to operate the air supply directly through the normallyopened contact of the master relay, a pilot fuel supply control means,the pilot fuel sup- 7 ply control means being connected in parallel withthe ignition, the timer motor and limit switch being connected inparallel with the clutch and these two circuits being connected inparallel with the air supply means.

9 thereby to provide pre-ignition, non-recycling, prepurge and pilotproving.

8. The combination as in claim 3 further characterized by the air supplymeans, the clutch, and the series circuit of limit switch and timermotor all being connected for energization directly by the normally opencontact of the master relay, and a pilot fuel supply control meansconnected in parallel with the control, thereby to provide fuel valvedelay, pre-ignition, non-recycling, prepurge and pilot proving.

9. The combination as in claim 3 further characterized by the seriescircuit of limit switch and timer motor being connected in parallel withthe air supply means, and means connecting said series parallel circuitfor energization directly by the normally open contact of the masterrelay, an additional limit switch adapted to be actuated by the timermotor and electrically arranged in parallel around the normally opencontact of the master relay, a second normally open contact of themaster relay connected to isolate the circuit for fuel valve, ignitionand clutch with respect to closing of said second limit switch aroundthe first normally open contact of the master relay, and pilot fuelsupply control means connected in parallel with the ignition, thereby toprovide fuel valve delay, pre-ignition, non-recycling, prepurge andpilot proving, and post-purge.

10. The combination as in claim 3 further characterized by the seriescircuit of limit switch and timer motor being connected in parallel withthe air supply means, and means connecting said series parallel circuitfor energization directly by the normally open contact of the masterrelay, an additional limit switch actuated by the timer motor andelectrically arranged in parallel around the normally open contact ofthe master relay, a second normally open contact of the master relayconnected to isolate the circuit for fuel valve, ignition and clutchwith respect to closing of said second limit switch around the firstnormally open contact of the master relay, pilot fuel supply controlmeans connected in parallel with the ignition, with the main fuel valvecontrolled through the series circuit of said second normally opencontact of the master relay, one of the cam contacts and the normallyopen contact of the flame relay, thereby to provide fuel valve delay,pre-ignition, non-recycling, prepurge, pilot proving and post-purge.

References Cited in the file of this patent UNITED STATES PATENTS1,986,032 Townsend Jan. 1, 1935 2,618,323 Aubert Nov. 18, 1952 2,655,207Outterson Oct. 13, 1953 2,655,208 Outterson Oct. 13, 1953 2,673,603Outterson Mar. 30, 1954 2,685,918 Marquardt Aug. 10, 1954 2,851,095Aubert Sept. 9, 1958

